Synthesis and properties of zwitterionic phosphonioglycolates

Abstract

Reaction of diphenylphosphane with glyoxylic acid hydrate in diethyl ether furnished diphenylphosphanylglycolic acid 1 and in a 1:2 molar ratio almost quantitatively the zwitterionic phosphonioglycolic acid glycolate 2. Tertiary phosphanes with aryl or alkyl groups (phenyl, m/p-tolyl, p-anisyl, n-butyl, tert-butyl) react similarly to triorganylphosphonioglycolates 3a–h, which like 2 precipitate from the etheral solutions of the reactants. Tri-n-butylphosphonioglycolate (3e) forms an ionic liquid and tri-tert-butylphosphonioglycolate (3f) a viscous product whereas the other phosphonioglycolates are solids. Yields and stabilities of 3a–e increase with the P-basicity of the starting phosphane whereas bulky groups like tert-butyl cause destabilization. Compound 2 is the most stable phosphonioglycolate with only minor amounts of 1 in the solvolysis equilibrium in D2O. The triaryl and tributylphosphonioglycolates 3a–f decompose in protic solvents with recovery of tertiary phosphanes. On heating at 100°C the compounds decompose to the corresponding phosphine oxides, minor amounts of glycolic acid and unidentified products.